With the continuous development and improvement of communications systems, people have increasingly high requirements on communication quality, that is, they hope to communicate well not only on the ground or in open space, but also in a relatively secluded place such as a basement.
Currently, one radio frame is composed of 10 subframes, and the 10 subframes are respectively numbered as subframe 0, subframe 1, subframe 2, . . . , and subframe 9. A 10 ms radio frame is used as an example; each subframe of the radio frame is 1 ms, and if a preamble sequence is also 1 ms, one preamble sequence may be sent within each subframe of the radio frame.
In the prior art, a process in which user equipment randomly gains access to a base station is the first step for the user equipment to implement uplink synchronization and establish a connection to the base station. In the process in which the user equipment randomly gains access to the base station, the user equipment randomly selects a preamble sequence that is from the base station and sends the preamble sequence to the base station, so that the base station sends, after correctly matching strength of the received preamble sequence with a preset strength threshold of the base station, a response message to respond to the user equipment, so as to enable the user equipment to gain access to the base station.
However, a preamble sequence sent by user equipment located in a basement or other user equipment with a relatively great link loss has a relatively great loss in a transmission process, which accordingly causes that the base station cannot correctly receive the preamble sequence or that signal strength of the received preamble sequence is relatively low, and as a result, matching cannot be correctly performed for the preamble sequence. If no response message is received by the user equipment from the base station within a preset time, the user equipment selects another random access channel to send a reselected preamble sequence to the base station, which makes the user equipment continually send a randomly selected preamble sequence to the base station; however, the base station still cannot perform matching correctly, thereby causing a decrease in a matching probability of the base station and a decrease in efficiency of gaining access to the base station by the user equipment.